1. Field of the Invention
The present invention relates to a decolorizable ink composition, namely, an ink composition capable of being decolorized by the application of heat thereto, and an ink jet printer using the above-mentioned ink composition.
2. Discussion of Background
With a recent spread of office automation, the volume of data to be processed has been rapidly increasing. For outputting such data, an enormous amount of paper is consumed as a recording medium. This causes a problem from the viewpoint of resource protection in the printing and copying fields.
To solve the above-mentioned problem, repeatable recording is demanded. Such repeatable recording has been investigated in the fields of electrophotographic recording and electrostatic recording. Further, an ink composition for recording and printing has also been studied to achieve repeatable recording.
Japanese Laid-Open Patent Application 4-362935 discloses a recording material capable of forming thereon images by recording or printing, which images can be erased from the recording material by the exposure to the near infrared rays. Another image can be again recorded or printed at the position from which the previous image has been erased. In this case, however, the recording or printing apparatus becomes necessarily complicated because the image erasure needs the near infrared rays. In addition, there is another problem that the printed image may not be completely erased even when exposed to the near infrared rays.
Japanese Laid-Open Patent Application 7-81236 discloses an ink composition which comprises a coloring compound, a color developer, and a desensitizer including an organic phosphoric compound having a decolorization action. A color image constituted of the above-mentioned ink composition formed on a sheet of paper can become colorless. However, it is still difficult to return the image-bearing sheet to the original state just like a fresh paper because of insufficient decolorization behavior of the ink composition.
Japanese Laid-Open Patent Application 10-88046 discloses a decolorizable ink composition comprising a coloring compound, a color developer, and a decolorization agent having the properties that can preferentially dissolve either the coloring compound or the color developer. An ink image prepared by this ink composition can be decolorized. However, the ink image cannot be perfectly erased, and the process for image erasure is very complicated because rapid cooling is required after heating.
Accordingly, a first object of the present invention is to provide an ink composition, in particular, suitable for a ink jet printer, capable of forming an ink image on a recording paper and erasing the ink image therefrom easily, rapidly, and completely, by the application of heat thereto, to such a degree that the recording paper from which the ink image has been erased can be repeatedly used.
A second object of the present invention is to provide an ink jet printer capable of carrying out image recording and image erasing simultaneously or selectively, with the structure of the ink jet printer being substantially equal to that of the conventional printer, aiming at light weight, thin and small size, and low cost.
The first object of the present invention can be achieved by an ink composition comprising a coloring agent, a color developer, a decolorization agent, and a solvent in which the coloring agent, the color developer, and the decolorization agent are dissolved or dispersed, the ink composition being capable of being colored at 40xc2x0 C. or less, with the coloring agent reacting with the color developer to form a chemically bonded structure, and also capable of being decolorized when heated to 100xc2x0 C. or more, with the chemically bonded structure being ruptured to liberate the color developer therefrom, and the liberated color developer being chemically bonded to the decolorization agent.
The second object of the present invention can be achieved by an ink jet printer comprising a paper feeding mechanism for feeding a recording sheet for ink jet printing, a recording mechanism for recording an ink image on the recording sheet fed from the paper feeding mechanism with the above-mentioned ink composition, and a paper discharging mechanism for discharging the recording sheet from the ink jet printer.
The above-mentioned ink jet printer may further comprise an erasing mechanism for erasing the ink image recorded on the recording sheet, the erasing mechanism comprising a heater, which is disposed along a passage for transporting the recording sheet between the paper feeding mechanism and the recording mechanism.